Process of manufacturing straw paper



CCL 4, 1932. P DREWSEN PROCESS OF MANUFACTURING STRAW PAPER v Filed oct. 13. 1930 ,Sca Z es Secafzaay 36a Zers ATTORNEYS fig;

PIERRE DREWSEN, OIE SANDUSKY, OHIO, ASSIGNOR 'IO THE HpINDE @t DAUCH FAPER COMPANY, OF SANDUSKY, OHIO, .A CORPORATION OF OHIO PROCESS OF MANUFACTURING STRAW PAPER Application led October 13, 1930.

The invention relates to the manufacture of straw paper and more particularly to that type used in the manufacture of corrugated wrappers and shipping containers. It is the object of the present invention to simplify the process by the elimination of one step `heretofore used as well as the apparatus required therefor. Itis a further object to shorten the time required in treatment yand to obtain a product having properties equal or superior to those of the product produced by the usual method. lVith these objects in view the invention consists in the construction as hereinafter set forth.

The drawing is a diagrammatic representation or flow sheet indicating the successive steps of my improved process.

In the present state of the art the method of manufacture of straw paper consists of three principal operations: First, the wheat, rye, oat or other straw is cooked in rotary digesters with alkali and water. Various formulas are used, some of them being approximately 5% lime and 5% 4soda ash based on the dry weight of the straw; or to 14% high calcium linie based on the dry Weight of the straw; ora mixture of caustic soda and sulphide of soda, the total chemicals used being about 4 to 7% based on the dry weight of the straw. The steam pressure used varies from to 60 pounds per square inch and the time of cooking from 6 to 10 hours, or over night, and about two or three pounds of water are used per pound of dry straw in the rotary digester. The second operation consistsl in beating the cooked straw and jordaning the same in order to draw out the fibres and reduce their length to make them suitable for the paper machine. During the beating operation the general practice is to wash the stock in order to remove as much ofthe spent cooking liquor as possible. The third operation consists in forming the beaten and jordanned fibres into a sheet on the paper machine according to the well known art in which cylinder or Fourdrinier paper machines are used.

The rotary di gesters used in the first operation hold approxxniately 14,000 pounds of dry straw per charge, but in order to intro- Serial No. 488,493.y

duce this quantity it is necessary to fill the rotaries with successive amounts of straw, each of which must be wilted down separately. F or example,` approximately 6,000 pounds 'of straw are introduced during the first till together with the water and cooking chemicals. The cover is then put on and the rotary is cooked for about one hour, more or less. The steam pressure is then blown down and an additional quantity of straw is introduced. The cover is then put on again and the charge is cooked for approximately one hour more. The steam pressure is then blown olfand a further quantity of straw introduced, and so on, for about five or six fills during the course of which a total of about 14,000 pounds of straw are introduced, provided there are'enough rotaries available to prepare sufficient stockA for a 24 hour run on the paper machine. -ln this case the introduction of this straw requires vapproximately a whole working day, consequently it becomes necessary to cook the'rotaries all night and to blow them down and empty them early in the morning. For a` mill maklng sixty or seventy tons of straw paper in twenty-four hours, it is necessary to have about sixteen or more rotary digesters available. This involves a considerable capital investment in digesters including drives for same, foundations, conveyors, buildings to house them, etc., and it also involves thelabor of nine or ten men in order to fill, empty and cook these' digesters, as well as to handle the cooked straw.v

In some mills however, there are not enough rotary digesters for one cook each per 24 hours. Where this is the case it is necessary to operate on as few as three fillsv of straw twice in Qi hours instead 'of von six iills once in 24 hours. This makes it necessary to approximately double the number of rotary house operators to supply enough cooked straw material to keep up with the demand of the paper machine.

In some mills it is the practice to empty the rotaries on a conveyor which heaps the cooked straw in a seasoning room from which itis manuallyforked or shovelled to another conveyor which brings/it into the beater line below,

room. The object of this seasoning is to soften the straw still further and to bring about a. certain mixing ot' stock from different rotaries.

Whether there are sufficient rotaries or not, the filling of these vrotaries with straw presents a problem which is caused by the bulky, nature of dry, baled straw and the length of time it takes to wilt it down to a smaller volume. In present practice this problem is met by employing a comparatively large number of men to stuff in the straw and b y using a large number of rotaries to wilt it down during the period allotted for this purpose. y

By means of the process which I shall out- I have found it possible to eliminate the entire rst operation mentioned above, namely, the use of rotary digesters in the manufacture of straw paper fior corrugated boxes. I have found that it is possible and practicable to reduce and wilt raw, dry

i straw in the rpresence of hot water and caustic alkali in a paper mill beater of the ordinary type. Approximately 1Q% alkah, more o r less, based on the dry weight of the strawpis added to the batch together with about 20 pounds of water per pound of straw. 'Ihe addition of straw to a beater is not essentialdiferent from the addition of pulp or paper stock, but it is essential in this process that the water in the beater be maintained at as high a temperature as possible, say 18 0 to 205 degrees Fahrenheit, and that caustic alkali be added. The length of time necessary in the beater is approximately one to two hours depending upon the water temierature and the efficiency of the beater. ubstantially dry, baled straw wilts down almost immediately under 4these conditions.

After the stock has been treated in beaters for this length of time I find it desirable, in

' the interest of economy, in order to conserve heat and chemicals, to effect as complete a separation of the hot caustic liquor from the straw substance as possible, and to return the hot caustic liquor to a storage tank from which it may be re-used in the beaters to treat additional quantities of straw, after which additional caustic alkali is added to this liquor to bring it up to the desired strength.

An Oliver filter or a Decker or any similar device may be used for this purpose. The amount of caustic to add to the re-used liquor can be determined by a simple calculation based on titratingl ak-nown amount o'f this liquor with a standard vacid solution using a suitable indicator, such as phenolphthalein, which anyone skilled in the practice of analytical chemical methods will understand.

The separation of the beaten stock from the caustic liquor may be made vmore complete by spraying the filtered iber with water while still on the cylinder mould of the Oliver, this wash water being combined with the filtered caustic liquor in such proportion that the total volumeof caustic liquor in circulation remains approximately constant.

The separated straw stock may then bev treated still further in beaters, or it may be passed directly to the Jordan engines from which it reaches the Fourdrinier or cylinder paper machine where the paper is formed, dried and calendered. This stock will necessarily contain some residual caustic, the presence of which may be injurious to the wool :felts of the paper machine. I find it desirable to neutralize at least a portion of this residual alkalinity to the point where the felts will be protected, by adding a stream of acid substance at the head box, vat or receiver of the paper machine. Sulphuric acid, if care- :fully controlled, sulpliurous acid, sulphate of alumina, sulphate of iron, nitre cake or any suitable acid material may be used for this purpose. In fact it is not necessary to neutralize this alkalinity to as low a pI-I as 7 .0, since experience demonstrates that a pH of 8.0 or higher maybe used on the machine wire without damage to the blankets orthe paperproduct. In fact, the more alkaline the stock is at the paper machinewire, the higher will be the crushing resistance of the corrugations in the finished corrugated sheet.

As diagrammatically represented in the drawing the straw from stacks or other source of supply is weighed on scales B and fed into a large breaker or beater tank C. The caustic received from a source D isv first introduced into a tank E and through `a measuring tankF into the beater tankC. If lime is used in the treatment, it is introduced from bags into the tank C.v After treatment in the tank C the material passes to the filter G in which the partially defibered pulp is sepics ing to a tank H from which it is returned to v the tank C. The pulp is passed on to a chest I from which it is introduced into the secondary beaters J J', thence to the chest K, tothe J ordan L and screen M to the head box vor vat N of the paper machine O. Neutralization is effected by an acid substance supplied from the tank P and introduced into the vat N.

In addition to the advantages incident to the elimination of rotary digester cooking, the costof additional men, and other financial overhead, the above described process pro diices a sheet of straw paper which is considerably superior `to those made by present methods, and in addition to this, my improved process oiers a more simple but vastly more eiicient means of control of both process'and iio soda, but no lime, in the hot water in the beaters. On the other hand, if a somewhat more bulky sheet of greater weight but lower strength is desired, as for instance for the so-called egg case filler, in other words, the soft yellow partitions frequently used to create individual compartments for eggs in shipping containers, or if a soft grade of corrugating paper is desired where high crushing resistance is not imperative, such paper can be made by eliminating the use of caustic soda entirely and using in its pla-ce approximately ten per cent of high calcium lime, based on the dry weight of the straw. Again, if a paper of strength somewhere between these extremes is desired, a mixture of say iive per cent caustic soda and five per cent caustic high calcium lime maybe used in the hot water in the beaters. Still another variation in my process would be t0 use varying mixturesvof caustic high calcium lime and soda ash, the interaction of which would produce caustic soda and calcium carbonate, and if an excess of lime were used, the straw would in this case be acted upon by caustic lime and caustic soda. One possible disadvantage of this variation for certain purposes would be the presence of insoluble carbonate which might reduce the' strength of the sheet; also the presence of carbonates may cause foaming if acid substances are used to neutralize excess alkalinity, as mentioned above.

Still another variationv to this process would be to increase or reduce the quantity of caustic soda above or below ten per cent, based on the dry weight of the straw, without using any lime at all. An increase in caustic soda tends to hydrate the straw substance still further and thereby to increase lthe moisture content of the sheet at the dryers of the paper machine which, while it results in reduced paper production, increases the strength of the paper. A reduction in the concentration of caustic soda in the beaters to say seven per cent results in a greater power consumption but produces a fibrous stock which separates from its water of suspension more readily on the wire of the paper machine. This property tends to increase the production of paper, which, however, has a lesser strength.

While it is im ossible to state definitely any iixed limits o crushing resistance of corrugated papers made by this process, on account of the natural variations produced by equipment differences and lack of uniformity of operating conditions among straw paper mills, nevertheless the following may give some idea of the said limits.

If 10% of high calcium caustic lime (CaG) based on the weight of the dry raw straw is used in the beater without any caustic soda (NaOH), a sheet of straw paper which square feet will, when corrugated on a regular Langston type corrugator of about three .175 inch arches per linear inch, produce a corrugated product which has a vstrength of about 200 Webb units. If 10% caustic soda without any lime, based on the weight of the rawydry straw, is used in the beater, a sheet of paper weighing only about .28 pounds per 1000 square feet, similarly corrugated, will yield to crushing under a force of 350 Webb units more or less. The former sheet of 200 lVebb units is comparable instrength with rotary cooked paper whereV lime alone-has been used, whereas the 350 Webb unit paper issuperior in strength to a sheet made from rotary cooked straw where caustic soda or the lime-soda ash mixture has been used. Such rotary-lime-soda ash sheets seldomexceed 300 Webb units even when they weigh 34 pounds per 1000 square feet. The superiority of this improved paper in strength and weight is therefore obvious, and the improved control of manufacturing operations is evident.

In straw paper mills it isfrequently the custom to utilize box board clippings, old papers, folded news, etc., as fibrous material which is mixed with the straw fiber to a certain limited extent. In the above description process and variationsof the same, old papers may be similarly admixed, although such blending tends todefeat one of the ob- `jects of this invention, namely, the production of a light, strong sheet.

What I claim as my invention is:

1. In the process of manufacturing straw paper, the step of simultaneously treating the straw with alkali and beating to separate the same into fibre bundles.

2. In the process of manufacturing straw paper, the step of introducing dry straw into a hot alkali bath and simultaneously xleating to separate the same into bre bun- 3. In the process of manufacturing straw paper, the introduction of the dry straw into a bath of caustic alkali, mechanically disintegrating the straw while in said bath to separate the same into libre bundles, separating a portion of the alkali solution with its dissolved impurities from the pulp and re-using the impure alkali solution for the treatment of additional straw.

4. In the process of manufacturing straw paper, the step of mechanically disintegrating the straw into libre bundles in the presence of from seven to twelve per cent caustic alkali based on the dry weight of the straw.

5. In theprocess of manufacturing straw paper, the step of passing the straw successively between beaters in the presence of hot water containing from seven to twelve per cent of caustic alkali based on the dry weight of the straw.

6. In the process of manufacturing straw paper, the step, of separating the straw into fibre bundles in the presence of Water heated from 150 deg-rees to 212 degrees Fahrenheit and containing from seven to twelveper cent caustic alkali.

'f'. In the process of manufacturing straw paper, the step of partially neutralizlng the alkalinity of the straw to a pH test of 8.0 or higher by the addition of acid.

8. In the process of manufacturing straw paper including the beating of the straw 10 in the presence of caustic alkali, the ste of filtering the partially debered pulp rom the partly exhausted alkaline liquor and returning the latter together with dissolved impurities for further use. 10 9. In the process of manufacturing paper from straw, the step which consists in wilting the straw continuously and rapidly in a breaker beater.

10. In the process of manufacturing paper from straw, the step of wilting the straw continuously and rapidly in a hot aqueous alkaline mixture in a breaker beater.

11. In the process of manufacturing paper o? from straw, the step which consists of treat- M ing substantially raw dry straw in a breaker beater with black liquor from an alkaline process.

In testimony whereof I aiiiX my signa- 30 ture.

PIERRE DREWSEN. 

